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Patterns of Expression of a Lolitrem Biosynthetic Gene in the Epichloë festucae--Perennial Ryegrass Symbiosis

February 2008 , Volume 21 , Number  2
Pages  188 - 197

Kimberley J. May, Michelle K. Bryant, Xiuwen Zhang, Barbara Ambrose, and Barry Scott

Centre for Functional Genomics, Institute of Molecular Bioscience, Massey University, Palmerston North, New Zealand

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Accepted 9 October 2007.

Lolitrem B is synthesized by Epichloë festucae in associations with Pooid grasses. A complex cluster of at least 10 genes (ltm genes) is required for its synthesis. An early step in this pathway is catalyzed by ltmM, a symbiosis-expressed gene. PltmM-gusA reporter gene analysis was used to monitor ltmM gene expression patterns in planta. The minimum promoter length required for high-level gusA expression in infected seedlings is in the range of 480 to 782 bp. gusA was expressed by the endophyte in all infected vegetative plant tissues and in epiphyllous hyphae. Spikelets from reproductive tillers were analyzed at different developmental stages. During pre-anthesis, gusA expression was observed in all infected floral organs except the immature gynoecium. In post-anthesis florets, gene expression occurred almost exclusively in the gynoecium. Expression of gusA by the endophyte was observed in germinating seeds 24 h postimbibition and seedlings older than 6 days postimbibition in hyphae from the mesocotyl to the tip of the emerging first leaf. This work provides a detailed analysis of the spatial and temporal expression patterns of a symbiosis-expressed gene in planta.

Additional keywords:Epichloë festucae, perennial ryegrass, secondary metabolites.

© 2008 The American Phytopathological Society